Pool is clear but bottom looks spotty and dirty

[rkrgk]

It makes sense that the overnight FC wouldn't change much with so little of the algae's surface area left exposed to chlorine.
I think Borate is a good choice - maybe a little higher.

Yeah, I was following PoolDocs writeup on increasing to 50ppm, I got only 5 boxes of borax last time, I am planning to add 5 more, thats the reason my pH was a little off too.

The pH might be getting a tad high (especially with 400 CH). Muriatic Acid is a good way to bring it back down - Be sure to read and understand:Using Muriatic Acid to Safely Lower Your Pool's pH.

I did reduce the pH to 7.4 in the last two days.

I also got the polyquat 60 from amazon. And planning to add and see if it makes any difference. and may be get some trichlor powder and sprinkle directly on top of the black spots and brush if I can.